This invention relates to packets in which a quantity of infusible or soluble material is held in a porous envelope which is immersed in liquid to prepare an infusion.
Such packets have the disadvantage that a significant proportion of the infused liquid remains in the packet unless and until the user squeezes it out. This can be an inconvenient and unpleasant operation, and infusion packets have been proposed which are provided with threads that can be pulled to contract the packet and express the surplus liquid, so that the user does not have to touch the packet itself.
In U.S. Pat. Nos. 3,396,032, 3,237,550, 2,986,269 and 2,878,927, the thread is looped centrally around the packet (as a double loop in the case of U.S. Pat. No. 3,396,032). The ends of the loop are secured to one end of the packet, typically by stapling in a manner which allows them to be drawn through the staple to tighten the loop and so contract a bag to squeeze out the surplus liquid. At the opposite end of the bag the loop must be securely located centrally of the packet at all times and for this purpose some of the known packets require a further staple (U.S. Pat. Nos. 3,396,032 and 2,986,269), which is a disadvantage both in the manufacture of the packet and in its use when the free movement of thread may be impaired. Alternatively that opposite end of the packet may be notched (U.S. Pat. Nos. 3,237,550 and 2,878,927), but the difficulty arises that the notching weakens the end seal of the packet, which is particularly important because the tightening of the loop of thread will apply additional stress at this point and bring the risk that the bag will burst and its contents be spilt. Increasing the width of the seal to avoid that danger leads to a wasteful use of material and, moreover, the consequent increase of size of the packet will usually be a disadvantage from the consumer's point of view.
Other proposals (U.S. Pat. Nos. 2,881,910 and 2,466,281) pass the thread through apertures in the walls of the packet and so avoid the need for a notch, but they have the disadvantage that the infusible material may leak through the apertures, whether before or during use.